1. Field of the Invention
The present invention relates to nonvolatile memory devices using variable resistive elements.
2. Description of the Related Art
Examples of a nonvolatile memory devices using resistance materials include phase change random access memory (PRAM) devices, resistive RAM (RRAM) devices, and magnetic RAM (MRAM) devices. Dynamic RAM (DRAM) devices and flash memory devices store data using electric charge, while nonvolatile memory devices that use resistance materials store data using a change in state of a phase change material (PRAM), such as a chalcogenide alloy; a change in resistance of a variable resistive material (RRAM); or a change in resistance of a magnetic tunnel junction (MTJ) thin film due to a magnetization state of a ferromagnetic substance (MRAM).
The following description uses a phase change memory cell as an example. A state of a phase change material is changed to a crystal state or an amorphous state while being cooled after a heating process. Since the phase change material in the crystal state has low resistance and the phase change material in the amorphous state has high resistance, the crystal state may be defined as set data or 0 data, and the amorphous state may be defined as reset data or 1 data.